My thoughts on Low power, remaps,dynos and carbon

[Andyuk911]

I thought it appropriate to post a few ideas on why some cars don't make the right power.

Most of this information has been what I have personally collected and/or told from a reliable source.

The first thing you must accept is the base line.....

The RS4 engine in the engine bay will not make the full 414bhp standard.

No doubt when Audi tested the engine, it would have been on a dyno rig with no pumps and possibly a different exhaust and intake airfilter.

So my base line for a healthy car is 370-390hp.

Golden rule number one, if you are going to have a remap, make sure you car is healthy. On a RR you should see the same shape as what has been published. If you see anything else your car has a problem and needs to be investigated. If you are given an amazing number after a remap check the shape and make sure you see the at wheel graphs. A Dyno operator can apply the handbrake when doing the 'coastdown', thus the Dyno software could see a greater transmission drag number .. so the at engine number will loook fab. No standard RS4 with a remap will ever exceed 400hp. If it does take it somewhere else spend the £35 and be prepared to be disappointed.

Fitting an ITG/K&N does not harm the power output of the car .. probably buys you 1-3hp.

Fitting a miltek or other after market catback exhaust will cost you power with a factory map(up to 0080, don't know about 0090 yet). Why, well it seems this engine is very sensitive to changes and the ECU holds things back.

So we now have clue number one ... the ECU is sensitive to changes ...

So lets move onto the carbon build up. Audi know all about this. It is a fundamental fact that Direct Injection engines produce carbon. Hence why the Wynn's product has been developed.

The reality is that performance is not damaged by the build up. How can I say this? RAudiguy's(never cleaned) car performs very close to Pippyrips car, which had been fully cleaned. Both run custom maps and have no cats ... they are the will above 400Hp boys ...

The carbon deposits can potentially causes a problems longterm or in some cases sooner. Silver's car had an injector problem more than likely a damaged injector. This also brings me to the point that Super unleaded petrol should always be used to help remove anything on the 'wet side' but obviously to allow the ECU to advance the ignition as much as possible. There is logic to say it is worth while filling an empty tank with BP102(£2.42per Litre) and then going for a blat at Brands Hatch. Not only does the fuel have excellent cleaning properties the ECU should really advance the ignition due to the golden nectar

So now we have a picture that this engine is complicated and very much an electronic beast. As the RPM increases and depending if in Sport mode or not, lots of things open. We have the tail pipe exhaust valves(these have been found to be stuck), we have the flapper valve in the airbox and also the tumble vanes in the inlet manifold. All of these items are operated by vacuum and controlled by the ECU.

So we have two potential issues either a pipe could be damaged/lever jammed or indeed the ECU NOT seeing what it expects so holds things back. Again the ECU is relying on input from sensors to see the correct environment for power to take off.

We have all heard of MAF's being replaced and also other sensors. some live in a very harsh environment. To me I would have thought either a sensor works or does not .. but clearly we have seen Oli's car with a duff MAF(fault shown) but the car still appear to run ok on the road....but down on power.

On the oil front, it has been proven that the engine beats the crap out of it. I changed mine at 2.5k miles and almost every 5k thereafter. This might be the reason my car dynoed well at SRR. Regular new oil will be less prone to the carbon deposits and will be a 'lighter 'vapour in the inlet.

For the cars not on the button, I have no doubt that the engines are mechanically sound/good, but have an external item/pipe broken or a duff sensor.

As far as mods go, there are now lots of options depending on your pocket, but you must start with a healthy car.

[sonny]

Great write up Andy, I agree totally with you.

[DavidRoss]

I realise i'm stating the obvious but rather than worry about dyno numbers, why don't you guys just hire out a stretch of road, get a load of you together and thrash it out. Forget 320hp or 400hp on the dyno- get some baseline cars ie e46 m3 and a few other cars between the 300-400hp range and have a few drags. It will certainly settle the argument. I cant for a minute see even the lowest powered Rs4's losing to an e46 m3 and you will have your answer?

[UNI555]

Excellent post Andy, very interesting and makes a lot of sense!

[Andyuk911]

David,

the cars with 'strange' shaped plots are the ones down on power...

I agree 0-100 would indicate a healthy car or not.

I am more interested in the diagnosis of the lower powered cars.

Andy

[SR71]

Andy,

The reality is that performance is not damaged by the build up. How can I say this? RAudiguy's(never cleaned) car performs very close to Pippyrips car, which had been fully cleaned. Both run custom maps and have no cats ... they are the will above 400Hp boys ...

But they did have different exhausts from the exhaust manifold back right? I still think that is too many variables to generalise regards the effect of cleaning...

Here is a graph showing some differences.

My car dynoed at 388hp, pippyrips at 390hp.

But my FATS times were better and the car was running up to 10 degrees more advance.

AntoRS4 says:

30% is exactly the extra pressure that you can have into the intake manifold if the engine is perfectly tuned to take advantage from the intake/exhaust pressure waves ( this is not reported on your bosch handbook )
to tune the lenght of intake and exhaust pipes, the volume of the plenum and the lenght of the ram pipe is not easy, you also need to take in consider the cam timing and overlap period,and last but not the least the intake and exhaust air temperature ( this change the sound speed and so the resonance frequencies) . If all the parameters are correct you will have some extra positive pressure points in the rpm scale.

Intake air temperature and exhaust pipes temperature are the first parameters that can change ouput values on a dyno.
Dyno software corrects the power output for the effect that temperature has on the air density sqrt( (273+ Tin)/( 273+15°) ) , but can not correct the effect of the resonances that can completely disappear if the temperatures drive the acoustic tuning inside the pipes.
I know that seems strange but you have to know that the positive pressure waves ( that run at the speed of the sound ) must fall exactly in the cam overlap time ( that is very short ) so just a little change into the sound speed will compromise the entire system.
This is the reason because you can repeat dyno runs with same output results on engines that don't take advantages from the acoustic induction system.
If you are able to mantain the intake manifold and exhaust pipes temperatures you will obtain the correct values also on a rolling road dyno ( not easy )

From my experience a stock RS4 engine, with clean valves, with polished and shaped intake ports can reach a 5/8% extra pressure and apx 420hp.
If valves are not clean the cam overlap time will be decreased near to 0 with the effects that you already know...your engine will lose the 8% intake extra pressure (so 8% in output power).
If you are so unlucky the exhaust back pressure wave that can not cross at all the cam overlap to reflect itself into the intake runners/plenum, will stop into the cylinder filling it with exhaust gas instead of clean air (with more power lost).

Race engines have very wide cam overlap periods because they don't have to take care about pollution effects.
A wide cam overlap period with correct pipes sizing can produce 30% and more extra dynamic pressure.

This is a clever car and there are no simple solutions to extracting more from it. Its already hard enough getting 414!

[klauster]

Andy - thanks for all your help so far. The noises Audi are making are very similar to your own, they are looking at pipes and sensors when my car goes back in early June.

[Andyuk911]

Jay,
both run miltek ...

I understand what you are saying ...but I am more keen to understand why some cars are so low..... I don't believe the carbon is the problem with these cars.

The post was to express my thoughts and why I thought them

If I wanted to extract the ultimate HP .. I would go the cleaning and polishing route with a cross flow heads and de-cat

[RSLS]

What differences have been identified between the performance / power curves of cars fitted with Flapped and Non-flapped Milltek Exhausts?

I personally believe that it's foolhardy to 'remove' the flaps, because this will prevent the ECUs from 'controlling' the back-pressure in the Mid-range and effectively suppress the ability of the Engine to produce Torque.

[pippyrips]

What differences have been identified between the performance / power curves of cars fitted with Flapped and Non-flapped Milltek Exhausts?

I personally believe that it's foolhardy to 'remove' the flaps, because this will prevent the ECUs from 'controlling' the back-pressure in the Mid-range and effectively suppress the ability of the Engine to produce Torque.

Andy,

Both jim and I have milltek centre and rears, but we have different downpipes..

RSLS - what flaps are you referring to? The backbox flaps?

[SR71]

Sure the solution to the cars making in the low 300's is not just a flow issue, I'm inclined to agree, although, to be honest, I have no feel for what type of difference acoustic tuning makes...

But I still don't feel that the community should be happy with ~380hp when the publicity says 414hp.

Audi publicity doesn't say "By the way, if you take your engine out of the car and dyno it, you'll get 414hp".

Its a bit like MP's saying their expense fiddling wasn't strictly against the rules.

No one who buys a car understands the power claims to be justifiable in those terms.

I love the car, it does almost everything I want it to, doesn't really have a competitor here in wind and rain swept South Wales, but it still ain't right, that I haven't got what it says on the tin.

I reckon the cheapest way to 414+ would be to drop a V6 2.7TT in....aren't MRC doing that for someone?

[mac4RS]

would be to drop a V6 2.7TT in

& I' sure alot cheaper than the MTM SC if you want more power!

[mac4RS]

Its a bit like MP's saying their expense fiddling wasn't strictly against the rules.

I'm with you here SR...

[RSLS]

RSLS - what flaps are you referring to? The backbox flaps?

Backbox Flaps.

[rAudiguy]

Hi Guys,

Sorry not been around for a while and have so many posts to catch up on thought I would start here.

Andy, good post mate. I think the main thing that really came from the RR day is that we discovered that these cars do have more issues than maybe we first thought?? Airflow being a major one. If your car is healthy then it would seem you should be running the 365 to 385 mark on RR, but quiet clearly a number of cars almost 50% of those who attended the RR day were below those figures and I have no doubt in my mind that this is down to an airflow problem and consequently the ecu is not happy, all be it in most cases it doesn't flag up an error in VAG com.

I think the point in Andy's post is why are so many cars not performing properly?? I'm not saying that I don't agree with what J is saying about the cars not hitting the magic 414 out of the tin because I am but this post I believe is more in the interest of why so many cars were down on power. If nearly 50% of the cars on the day were not hitting the so called standard numbers of 365-385 how many others aren't? And bear in mind apart from Mac nobody had mentioned they thought something was wrong with their cars, even Oli didn't know he had a problem. (that's not a dig Oli just a fact ) My question would be how many other cars out there are not running properly. We have all seen posts on here from guys running 300bhp in an Astra's and other hot hatches saying he was as fast as an RS4 and we all get on the defensive calling the guy a troll etc. But the reality of this could very well be that if he raced a car which was only pushing out 300bhp which we all know is the case with some people, Mac Oli etc this could explain some of these results we have seen posted on here. Of course many of us myself included have shot this down because our cars are healthy and are producing late 300's/400bhp

Of course this doesn’t answer the question of why are so many cars are not running properly? Fingers crossed Mac, Oli and Nick will get some idea in the next few weeks from Audi and then who knows maybe and national recall will be needed. Lol

Jim